The development of improved processes for manufacturing non-volatile memory cell devices in the CMOS technology field requires the use of lower and lower supply voltages, in some cases close to 1V. In particular, very low supply voltage values are necessary for the use of thinner and thinner oxides. Also, the improved processes should limit as much as possible power consumption in the so-called “design low power” field.
Nevertheless, there are some requirements that remained basically unchanged despite the evolution in technology which is in contrast with these requirements. On one hand, there is a need to bias memory cells with drain voltages that are almost constant when technology varies (equal to 1V) in order to keep the current passing through the memory cells in the reading step high. On the other hand, there is a need for low access times even with high capacitive loads due to the large memory cuts required. These two factors make it difficult to manufacture a sensing circuit that is capable of performing a correct bias and I/V conversion for a memory cell in a limited voltage range (Vx).
A known sensing circuit, with traditional memory cell bias, is schematically shown in FIG. 1 and is globally indicated by reference numeral 1. In particular, the sensing circuit 1 is connected to a non-volatile memory cell, illustrated by an equivalent current Ic generator 2 connected to a first voltage reference, such as ground GND.
Moreover, the sensing circuit 1 is connected to a second voltage reference, such as the supply Vdd, by way of a load 3. The following relation applies to the sensing circuit 1:Vx=Vdd−VBL  (1)where Vdd indicates the circuit supply value and VBL indicates the drain terminal bias voltage of the memory cell corresponding to a voltage value in the contact point between the cell 2 and the sensing circuit 1.
In known memory devices, particularly in flash memories, the voltage value Vx provided by the above-mentioned relation (1) can be equal, and by way of example, even to only 200 mV. The sensing circuit 1 is difficult to manufacture for a correct bias of the load 3.
Moreover, to compensate for the reduced drive-capability due to the low supply voltage, it is often necessary to use particular transistors, such as natural transistors. However, these transistors have a higher cost linked to the number of process masks used for their manufacture.